1. Field of the Invention
The present invention relates to an encoder. Specifically, the invention relates to a system for a scale having an incremental channel and a reference mark channel and a reading head. Furthermore, the invention provides an encoder that can perform high-speed origin position detection based on a reference mark.
2. Description of the Related Art
Up to now, an encoder configured to measure a relative position of two members including a scale and a reading head has been provided with a scale on one member which includes a scale line and a reading head provided on the other member.
An optical scale reading apparatus includes an irradiation unit configured to irradiate a scale with light and a detection unit configured to measure and output a displacement of the relative position of the reading head in accordance with a reflection pattern generated by the scale irradiation.
A scale having marks in a periodic pattern is an incremental scale and generates an orthogonal signal on the basis of the periodic pattern of the incremental scale. A reference mark is provided in this scale, and an incremental counter is reset in a case where the reading head detects the reference mark.
Accordingly, the relative position of the two members can be confirmed.
In a system of a large number of encoders in the related art, a configuration in which an origin detection pattern of the scale is detected by moving a movable part to reset the incremental counter is adopted.
In an encoder disclosed in Japanese Patent No. 4274751, an origin signal is output in synchronism with an orthogonal signal.
However, the above-described encoders in the related art have the following problems.
That is, detection timings for the signal from the origin detection pattern and the orthogonal signal are shifted by a relative speed of the scale and the reading head, and for example, the position of the origin may be shifted in a case where the origin is detected at a low speed and a case where the origin is detected at a high speed. In that case, a relative value between the scale and the signal reading head has an error.
The present invention has been made in view of the above-described problems and provides an encoder that can stably perform origin detection even in a case where the origin detection is performed at a high speed and a movable body that can perform origin reset at a high speed.